Biology

Types of joints

What are the joints?

The joints are the joints that have bones to each other, which enable the movement of them there . If it weren’t for them, the bones would be still and no limb could be mobilized voluntarily.

The cartilages are the parts that enable these movements, generating your bones a stability without interfering with normal operation. They have an important flexibility and stretching capacity , which allows them to be developed for the practice of sports, especially those of high physical demand.

The arthrology is the branch of anatomy that is dedicated to the study of these joints, which appear in the head, chest, spine and all members of the body. The osteoarthritis or osteoporosis are related to bone diseases in which the joint function becomes decisive.

Classification of joints

There are two classifications that can be made regarding the joints. It will be seen that the joints allow a large, limited, or almost no amount of movement . According to that there is an important classification, as follows:

– Synarthrosis : They do not allow any movement.

– Anfiatrosis : Limited movement, in a single axis.

– Diarthrosis : They have a great capacity for movement, in more than one axis.

But mainly, the classification of the joints is done according to their structure :

Sutures : In the bones of the skull, the edges are irregular and interlocking. Also in this group appear joints in which the fusion of the bones is the union.– Fibrous joints : The bones that make up this type of joint are closely attached to the connective tissue , making it difficult to move very easily. They have a subdivision:

  • Gonphosis : Joints in the roots of the teeth (between the jaws, the jaw and the teeth) that join the two bones with the so-called periodontal ligament . This tissue degenerates over time.
  • Syndesmosis : Joins bones separated by a wide distance, so the amount of connective tissue is much greater than in the previous one, and it is arranged as a kind of lamina .

– Cartilaginous joints : The union of the bones comes strictly from the fibrocartilages , or the hyaline cartilages. They are also internally subdivided:

  • Symphysis : The bones contain two layers : one of cartilage and another of fibrocartilage . The movements that this type of joint can perform are very   limited , through compression of the connective tissue.
  • Synchondrosis : The material that joins the bones is pure cartilage . When the longitudinal growth of the bone stops, the cartilage is replaced by bone tissue, and they become fibrous type joints. They predominate in the thorax or in the spine .

– Synovial joints : They are those that allow the greatest amount of movements, due to the so-called synovial fluid that they have inside. This liquid also provides nutrients and reduces friction. An injury to such a joint is very difficult to repair. They have an internal subdivision:

  • Sliders : Allow side-to-side and front-to-back movements, limited by the restrictions of the adjacent flat bones (in parts of the body such as the clavicle, hands or feet)
  • In hinge : Fewer moving, allow only movement in one direction and can only be extended and flexed. Fits on a concave surface.
  • Elliptical : In bones that have a particular egg shape, such as those of the forearm or some of the wrist. The movement is quite free, with extension, abduction and flexion.
  • Pivotal : The articular surfaces are molded in a shape similar to a pivot, formed by the combination of a bone and a ligament . The movements are limited on the axis itself (rotation). The joints of the neck or forearm belong to this group.
  • Saddles : The surface of the bone has that concave shape, which allows another bone to ‘sit’ on it. The projection fits, making possible a very large amount of movements including the basic ones of the hand or fingers.

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